The present invention relates to cranes or analogous machines wherein an elongated boom, preferably an extensible and contractible boom, is movable about at least one axis (e.g., about a vertical axis and about a horizontal axis) so that its free end portion can be moved to a plurality of levels as well as in a plurality of horizontal planes. More particularly, the invention relates to improvements in attachments which can be separably or even permanently secured to the free end portion of the boom of a crane or a like machine to enhance the versatility of the machine by enabling it to carry out operations which are not expected from a conventional crane, scaffolding, fruit picker or the like. For example, a crane or an analogous machine which is equipped or combined with the attachment of the present invention can be utilized to move one or more workers close to the facedes of tall buildings, below the undersides of bridges or viaducts, adjacent to selected portions of tall chimneys or masts, adjacent to any selected portion at the exterior of a watercraft or aircraft, and/or adjacent to steep surfaces of cliffs or the like.
My copending application Ser. No. 793,970 discloses an attachment which is connectable to the free end portion of the boom of a crane or the like and includes a pivot bearing separably coupled to the boom, a second bearing pivotable in or relative to the pivot bearing about a horizontal axis, an elongated upright column which is reciprocable in the second bearing, and a gallery which is adjustably mounted on the column and is designed to carry one or more persons. The boom is preferably extensible and contractible and can also change its inclination in a vertical plane as well as about a vertical axis which is adjacent to or intersects its lower end portion. This enables the boom to move the gallery to hard-to-reach locations. A cable or the like is used to move the column up or down with respect to the second bearing so as to further enhance the versatility of the machine. Since the gallery is designed to accommodate at least one person and often a substantial number of persons, it is necessary to equip such machines with highly reliable safety devices which prevent the column and the gallery from becoming detached from the remainder of the attachment and/or from the boom in the event that the cable breaks. In the absence of such safety devices, attachments of the above outlined character would be banned by the relevant authorities in many countries, states, districts, cities, townships or other administrative units.